Two of our Crazyflie 2.0s are reading incorrect roll and pitch values when connected to using cfclient: one of them reads nothing at all, and the other is a slowly drifting upside-down-ish value that doesn't respond to tilting the unit. I've reflashed the firmware on all of our CFs with the latest release, and these two persist in showing this issue. They appear to start up fine, I can connect to them fine, but something is clearly very wrong with the output from those sensors. I'm not sure how to approach debugging this: any suggestions?

(These are used to teach programming in a public library, so they live pretty hard lives! Almost certainly they have been involved in repeated high speed encounters with the wall. Of course, so have the other half dozen working ones...)

If I understand it correctly they pass the self test? Have you checked the console output in the cfclient?

It could be damaged sensors but they are pretty robust. Higher chance of soldering cracked. If you(or someone else) have access to a hot air reflow station you can try to reflow the sensor chip. That would be the quickest solution to try and we have made a small video showing how to do it. Else drop us an email at support@bitcraze.io and we will work something out!